The skin prevents water and other various components in living bodies from being lost. It plays roles of preventing water from dissipating and of constantly maintaining a body temperature. Skin also functions as a barrier for protecting bodies from external physical and chemical stimulators (e.g., humidity, temperature, ultraviolet rays, etc.) and from various bacteria. Its physiological functions in the activities of living bodies are therefore very important. Keeping healthy and beautiful skin is also a subject of a great concern, especially, for female. Conditions of skin, however, are constantly affected by various factors such as humidity, temperature, ultraviolet rays, cosmetics, age, diseases, stress, food customs, and the like. A number of skin troubles, such as deterioration of various skin functions, aging of the skin, and the like, are caused by these factors. Among these, troubles such as dry skin, fatty skin, dandruff, and the like are caused by thickening of the skin, incomplete keratinization, abnormal lipid metabolism, and the like resulting from the progress in turnover of epidermis which is induced by external and internal factors affecting the skin.
Major conventional methods of preventing the skin troubles and improving the skin have been preventing the skin from drying or promoting its moisture retention capability by the application of synthetic or natural moisturizing components, improving blood circulation in the skin by the application of blood circulation promoters, and the like.
These methods, however, involve various problems relating to their effects on the skin trouble prevention or the skin improvement, duration for which the effects last, stability and safety of drugs, and the like.
Development of a composition for external skin care which is safe and has a superior keratin improving effect has therefore been desired.
On the other hand, wrinkles are produced by aging of the skin due to senility, exposure to sun light, and the like. Cells constituting fibroblost synthesizing dermal fiber components decrease and become small due to exposure to sun light and along with age. Especially, a large amount of colagen fibers are lost, leading to dermal degeneration and reduction in the dermal fat organization, and finally to the skin aging. This is a major cause of wrinkles, atony, and loss of flexibility.
A number of compositions and methods have been proposed for suppressing or curing aged skins such as wrinkles and the like (Japanese Patent Laid-open (ko-kai) Nos. 185005/1987, 502546/1987, 72157/1990, 288822/1990, etc.). Most of them, however, are not satisfactory in their effects of wrinkle improvement.
Vitamin A acid has been confirmed to exhibit a wrinkle curing effect [Journal of the American Academy of Dermatology, Vol. 25, No. 2, Part 1, 231-237 (August, 1991); ibid. Vol. 21, No. 3, Part 2, 638-644 (September, 1989); ibid. Vol. 19, No. 1, Part 2, 169-175 (July 1988); ibid. Vol. 15, No. 4, Part 2, (October, 1986)]. Vitamin A acid, however, has problems in its safety; e.g., it induces red spots on the skin, is irritative and teratogenic.
Development of a safe composition for external skin care exhibiting an excellent wrinkle curing effect has therefore been desired.
Some compounds among amine derivatives represented by the following formula (1), ##STR2## (wherein R.sup.4 is a linear, branched, or cyclic saturated or unsaturated hydrocarbon group having 4-40 carbon atoms, and R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6 are individually a hydrogen atom or a hydrocarbon group having 1-10 carbon atoms, either substituted or unsubstituted by 1 or more hydroxy groups) are known to be useful as an emulsifier [Journal of Colbid and Interface Science, Vol. 64, No. 2, 300-310 (1978), Japanese Patent Laid-open (ko-kai) No. 117421/1979]. It is also known that these compounds may be added to cosmetic compositions in an amount of 0.1-30% by weight [Japanese Patent Laid-open (ko-kai) Nos. 135233/1979 and 147937/1979]. However, there are no knowledge about the actions of said compounds (1) to the skin; especially their actions effected to dermal cells in the skin have not been known at all.
Based on the supposition that the wrinkles and keratinization of the skin are produced by abnormalities in functions of the skin organization, which are caused by various factors externally or internally affecting living bodies, such as environmental changes, e.g., change of climate, ultraviolet rays, etc., variations in physiological functions, e.g., those due to aging, diseases, etc.), the present inventors have studied various compounds as to (1) their capability of suppressing the progress in epidermal turnover, resulting in skin thickening, incomplete keratinization, abnormal lipid metabolism, etc., which are caused by ultraviolet rays, various components, etc.; and their capability of normalizing the keratinized skin, (2) their wrinkle improving capability, (3) their safety, and the like. As a result, the present inventors have found that amine derivatives of the above formula (1) and their acid addition salts exhibit these capabilities even in a very small amount, and thus are useful as a component for compositions to be applied externally to the skin. The findings have led to the completion of the present invention.